The present invention relates to a head actuator of a magnetic recording disk drive.
A magnetic recording disk drive is a system for performing recording/reproduction of information by scanning a magnetic head over a rotating ferromagnetic medium, or a magnetic recording disk, and is widely used as the center of storage devices for supporting the modern information age. The magnetic head is contained in a slider, which is flying over the magnetic recording disk with a gap on the order of nanometers therebetween at the time of recording/reproduction. A driving force for moving the magnetic head to a predetermined position is generally generated by a voice coil motor (VCM). The coil of the voice coil motor is connected to an arm rotatably supported by a pivot, and, further, a magnetic head slider is attached to the tip end of the arm via a suspension which consists of a load beam and a gimbal. The load beam is a spring member for generating a load which balances with the flying height of the slider, and the gimbal is a spring member which supports the slider and which absorbs the inclinations arising from assemblage and the surface oscillations of the disk without spoiling follow-up performance for tracking, by undergoing elastic deformations in the directions other than planes parallel to the disk surface. With this constitution, the magnetic head can be moved to a predetermined track on the rotating disk while maintaining a stable condition.
In recent years, the recording density of the magnetic recording disk drives has been enhanced (i.e., the track width has been reduced) more and more, and, since the magnetic head must be accurately positioned on the narrow track, it is necessary to enhance the accuracy in positioning the head. Conventionally, the positioning of the head has been conducted by only a large actuator such as the above-entioned voice coil motor; however, this system does not have a sufficient precision for the narrowed track width. In view of this, a mechanism for high-precision positioning or a micro-actuator has come to be indispensable for high recording density disk drives.
A variety of micro-actuators have hitherto been proposed for achieving the high-precision positioning, and they can be generally classified, on the basis of driving force, into three types, i.e., (1) electrostatic force, (2) electrostriction of piezoelectric material, and (3) electromagnetic force.
The conventional micro-actuator utilizing the electrostatic force of type (1) above (Fujita et al., IEEE TRANSACTIONS ON MAGNETICS, Vol. 35, No. 2, March 1999, pp. 1006-1010) has a structure in which a pair of mesh form electrodes are arranged between the gimbal and the slider, and the actuator portion is produced by Ni plating, thereby promising good productivity.
However, since the weight of the slider portion is too large as compared with the electrostatic force generated, resonance occurs at around 1 to 2 kHz, so that the servo band cannot be enlarged.
As a countermeasure against this problem, it may be contemplated, for example, to make the actuator itself as a capacitor and feed back the signal; however, such an approach would complicate the system itself. Thus, this system has not yet been put to practical use.
The conventional micro-actuator utilizing the piezoelectric material of type (2) above (Evans et al., IEEE TRANSACTIONS ON MAGNETICS, Vol. 35, No. 2, March 1999, pp. 977-982) has, for example, a structure in which two piezoelectric elements are disposed in a pair in the vicinity of a voice coil motor arm of the suspension. When voltages are impressed in such directions that the piezoelectric element on one side extends and the piezoelectric element on the other side contracts, the head is rotated in the direction of the piezoelectric element on which the voltage in the contracting direction is impressed.
In the conventional actuator utilizing the piezoelectric elements, however, depolarization of the piezoelectric elements occurs due to time variation or the like, with the result that the displacement per voltage is reduced gradually. Therefore, there is the problem that a predetermined stroke cannot be obtained after use for a somewhat long time.
Furthermore, the conventional actuator utilizing the piezoelectric elements has the demerits of low productivity and high cost. Because of the above-mentioned problems, the actuator utilizing the piezoelectric elements has not yet been put to practical use.
The mechanism utilizing the electromagnetic force of type (3) above promises a high productivity due to simplification of structure, a comparatively large stroke, and a high reliability. A conventional micro-actuator utilizing the electromagnetic force in which a tip end portion of an arm of a voice coil motor being a coarse actuator is made to be a stator of the micro-actuator and a suspension rotatably attached to the tip end of the arm is made to be a rotor, has been proposed (Koganezawa et al., IEEE TRANSACTIONS ON MAGNETICS, Vol. 32, No. 5, September 1996, pp. 3908-3910). However, such a structure in which a shaft and the like are provided has the problem that the structure of an attachment portion is complicated and the productivity is low.
Furthermore, a micro-actuator has hitherto been proposed in which a stator is provided on a load beam, and a slider mounted on the tip end of a suspension via a hinge is driven by a long rotor extending from the stator portion to an upper portion of the slider (U.S. Pat. No. 6,295,185). In such a structure, however, compatibility of elasticity in the driving direction and translational rigidity in the vertical direction are difficult to secure for the hinge, so that resonance would occur in a low frequency region, and servo band cannot be enhanced. Further, since the rotor makes frictional contact with the load beam or the like at least in the vicinity of the hinge, it is inappropriate to mount such an actuator in the inside of the magnetic recording disk drive in which a clean atmosphere must be maintained.
On the other hand, a micro-actuator has hitherto been proposed in which both sides of a rotor disposed between a slider and a gimbal and so fixed as to surround the slider are connected to an attachment portion for attachment to the gimbal through very small leaf springs (called micro-beams) (U.S. Pat. No. 6,078,473).
In this actuator, a stator is disposed at the attachment portion for attachment to the gimbal or at the gimbal portion. In this structure, by regulating the material for the micro-beams, the number of the micro-beams, the aspect ratio of the section of the micro-beams, and the like, it is possible to simultaneously secure both elasticity in the driving direction and translational rigidity in the other directions, so that the servo band of the actuator can be enlarged, and positioning precision can be enhanced.
However, the micro-beams of the micro-actuator are produced as one body with the slider attachment portion and the rotor portion by deep etching of a single crystal of silicon, and the etching depth is as large as 100 to 200 μm, so that the productivity is low.